MG132 is a specific, potent, reversible, and cell-permeable proteasome inhibitor (Ki = 4 nM) . Reduces the degradation of ubiquitin-conjugated proteins in mammalian cells and permeable strains of yeast by the 26S complex without affecting its ATPase or isopeptidase activities. MG132 activates c-Jun N-terminal kinase (JNK1), which initiates apoptosis. MG132 also inhibits NF-κB activation with an IC50 of 3 µM and prevents β-secretase cleavage.